Two different set of soil samples were collected near Kaduna Refining and Petrochemical Company Limited (KRPC), a Subsidiary of Nigerian National Petroleum Corporation (NNPC) Kaduna. The first set of samples labelled (D) was obtained from areas where diesel from the refinery spilled into the environment and the second set of samples labelled (P) was collected from areas where petrol leaked and spilled into the environment. The pH of the soil was found to be 5.9 and 6.2 for D and P samples respectively. The cation exchange capacity (CEC) was higher in sample P than in sample D (32.0 and 30.0 mmol/kg of soil respectively). P has high concentrations of cations ( Ca2+, Mg2+, K+ and Na+ with concentration values 3.6, 1.17, 0.50 and 0.22 mol/kg respectively) because of its high CEC while sample D with a lower CEC has a lower concentration of cation (Ca2+, Mg2+, K+ and Na+ with concentration values 1.20, 0.27, 0.25 and 0.17 mol/kg respectively). The oil (contaminant) was extracted in dichloromethane and a GC-MS analysis was run to determine the nature (composition) of the oil and the concentration of the contaminant was determined using gravimetric method. Results revealed that the total concentration of the contaminant (oil) before treatment was 398 g/kg and 194 g/kg for sample D and P respectively. The GC-MS results obtained showed that in both samples (D and P) linear and branched alkanes(n-Tetratetracontane, 3,6-Dimethyldecane, n-Pentadecane, 2-Bromodecane, n-Heptadecane etc. and n-Tetradecane, 2-Bromododecane, n-Octadecane, 14-Methyl-8-hexadecenal etc. respectively) were the main contaminants. Bioremediation was initiated and examined by applying separately fertilizer (F), bacteria inoculation (B), emulsifier (E) on the contaminated soil and by combining bacteria inoculation and fertilizer (B and F), fertilizer and emulsifier (F and E), bacteria inoculation and emulsifier (B and E) also a combination of bacteria inoculation, emulsifier and fertilizer (B,E and F) on both sample D and P . Bioremediation was determined by weight lost method throughout the 28days of treatment and the trend of degradation is thus: (B, E and F) > B > ( B and E ) > (B and F) > (E and F) > E > F. Results obtained showed that treatment with B,E and F combined together yielded the highest percentage of oil degradation (97%, and 95% for samples P and D respectively), followed by B (96% and 81% for samples D and P respectively). This finding suggests that Bacillus sp is a viable microbial strain for bioremediation of oil-contaminated soil when biostimulated by adding fertilizer combined with emulsification (B, E and F). The percentage of oil degraded in sample P and D are almost the same (97 and 95% respectively) and there is significant difference (P < 0.05) in the trend of degradation for D and P this may be because, even though the samples contained oil (contaminant) with almost the same composition but differ in the number of carbon chain and other physical factors like density, viscosity etc.
One of the major environmental problems in the world today is hydrocarbon contamination resulting from the activities related to the petrochemical industry. In Nigeria, oil pollution problems have been prevalent since the commencement of oil exploration and development of the petroleum industry (Okoh et al., 2001). Accidental release of petroleum products are of particular concern in the environment. Hydrocarbon components have been known to belong to the family of carcinogens and neurotoxic organic pollutants. Currently accepted disposal methods of incineration or burial insecure landfills can become prohibitively expensive when amounts of contaminants are large. The deleterious effect of pollutants on the environment has led to increased awareness and vigilance against contamination of the Niger Delta environment. In relatively recent times in Nigeria, there has been remarkable increase in population, urbanization and industrial activities, (Eze and Okpokwasili, 2010). The release of crude oil into the environment by oil spills is receiving worldwide attention (Millioli et al., 2009). Bioremediation which has been defined as biological response to environmental abuse has continued to receive research attention across the globe (Hammer, 1993). Bioremediation has been described as the use of living microorganisms to degrade environmental pollution. In order words, it is a technology for removing pollutants from the environment thus restoring the original natural environment (Sasikuma and Papmazath, 2003). The long term aim of bioremediation designs is to present cost effective designs which reduces the pollutant to a level referred to as low as reasonable and practicably possible (ALARP). In order to achieve this cost effectiveness, researchers all over the world have begun to pay research attention to the use of organic waste as the source of limiting nutrients for effective bioremediation (Ibiene et al., 2011).
Mechanical and chemical methods generally used to remove hydrocarbons from contaminated sites have limited effectiveness and can be expensive (Das and Chandran, 2011). Bioremediation is the promising technology for the treatment of these contaminated sites since it is cost-effective and will lead to complete mineralization. Bioremediation functions basically on biodegradation, which may refer to complete mineralization of organic contaminants into carbon dioxide, water, inorganic compounds, and cell protein or transformation of complex organic contaminants to other simpler organic compounds by biological agents like microorganisms (Das and Preethy, 2010). Many indigenous microorganisms in water and soil are capable of degrading hydrocarbon contaminants.